A conventional screen printing apparatus such as disclosed in Japanese Patent Document 1 below includes a machine frame which is sectioned into a workpiece introducing section and a workpiece printing section. Upper and lower printing tables are alternately moved between the workpiece introducing section and the workpiece printing section, wherein loading or unloading of a workpiece into or from the printing tables and a screen printing process of printing patterns on the workpiece can be simultaneously carried out at the workpiece introducing section and the workpiece printing section. The upper and lower printing tables are moved horizontally on rails provided at upper and lower levels for the upper and lower printing tables respectively between the workpiece introducing section and the workpiece printing section.    Patent Document 1: JP-2007-62205 A
In a conventional screen printing apparatus, the upper and lower printing tables, respectively, run on rails horizontally extending at vertically different levels without interference from each other. This means that for example, the operations of unloading of a processed workpiece, the loading of a unprocessed workpiece and the setting of the unprocessed workpiece with respect to the upper and lower printing tables are manually carried by a worker at different working levels. Those operations are troublesome to the worker, and may lay physical and mental burdens on the worker.
Even in an automated system, various operations including the loading and unloading of workpiece in the introducing section, setting of a CCD (charge coupled device) camera unit, positioning of a printing frame and a squeegee unit for aligning them with the workpiece and vertical movement of the printing frame and the squeegee unit in the printing section must be controlled in different manners with respect to workpieces set on the upper and lower printing tables from each other. This requires complex programs for a system control unit.
The present invention provides a method of alternately moving two printing tables between a workpiece introducing section and a workpiece printing section in a screen printing apparatus. The printing tables can be located at the same level in both of the workpiece introducing section and the workpiece printing section without any interference from each other during the alternate movement of the printing tables to thereby lighten the burdens on the worker and make programs for a system control unit simple.
The present invention also provides a table driving unit for executing such a method.